Information recording



United States Patent 3,140,143 INFORMATION RECORDlNG Alfred F. Kaspaul and Erika E. Kaspaul, Stamford, Conn.,

This invention relates to processes for recording information and more particularly to a process for producing a visible permanent record by the selective evaporative deposition of metals upon certain substrates.

It is known that metals can be deposited by evaporation upon various substrates, and that selective deposition of metals can be achieved by prenucleating areas of the substrate upon which the metal is to be deposited with other metals. Such techniques are described in US. Patent 2,833,257 to H. G. Wehe, as well as in other reports and publications.

The processes used for selective deposition of metals in the past have employed various meansfor producing the prenucleated image, which forms the invisible, latent image upon which the metal is deposited toform a visible permanent record. For example, electron beams which are modulated in sweep and intensity have been employed to scan the surface of substrates, to produce a charge pat tern, upon which a prenucleating metal ion is deposited as a latent image. Another approach has been toevaporate metals having relatively high melting point through a pin hole, to produce an invisible latentimage of the metal source, for example, a coiled filament. Such latent images are developed by vapor coating the substrate with a metal to produce a visible record in the areas where the latent image exists. The electronic methods of forming the latent, invisible image require relatively expensive and complicated apparatus, while simpler devices heretofore known employing pin hole type cameras are limited in their scope of operation. Both types require operation under greatly reduced pressure. So far as is known, such techniques of recording have not found practical use today.

It is an object of this invention to provide a process for recording images corresponding to intelligible patterns (herein termed information) in which an invisible latent image which is later developed by metal vapor deposition thereupon is formed under atmospheric pressure and without the use of expensive special equipment. It is another object of this invention to provide a process for producing a permanent, visible metallic record of information upon certain substrates. Other objects of the invention will be apparent from the disclosure made hereinafter.

In accordance with the above and other objects of the invention, it has now been found that an invisible latent image corresponding to intelligible patterns can be formed upon a substantially inert, substantially anhydrous solid substrate which has an inorganic'metal compound as a part of the surface thereof, by depositing at least trace amounts of an aqueous liquid on the substrate in the areas in which an image is to be formed. In this way, an in visible latent image is formed which can then be developed to a visible image which is a record of the predetermined information at any desired time by selective vapor deposition of a metal chosen from Group II-B of the Periodic System thereupon, using standard processes for vapor deposition of metals.

Substrates which can be used for the deposition of the latent image, and which are subsequently useful for production of the permanent visible record upon the image portions, are those materials which contain inorganic metallic compounds upon or as a functional part of their surfaces, and which do not contain substances which will cause appreciable evolution of gas at the temperatures and pressures at which vapor deposition of the image forming metal is to be deposited thereupon. By the term functional as used herein it is intended to define the role of the metallic compound as participating in the formation of the invisible latent image. To this end, sufficient amounts of the compound must be accessible at the surface to permit of some interaction with the aqueous, image-forming fluid.

The metallic compounds are useful as part of the surface of the substrate are preferably substantially insoluble in water, and at least of low water-solubility, and in: clude metallic oxides, sulfides, and halides, for example, cadmium sulfide, barium sulfate, zinc oxide, cuprous chloride, cadmium selenide, titanium dioxide, cadmium oxide, zinc sulfide, silver oxide and the like. These are ordinarily used in finely divided form. Various means are known for production of surfaces of this type. For example, the metallic compound which is selected can be incorporated into a binder, e.g. a Pliolite, a resinous copolymer of butadiene and styrene. Other resinous binders suitable for the purpose include chlorinated rubber, polystyrene, polyvinylidenechloride, polyvinyl butyral and the like. Alternatively, the metallic compound can be incorporated into a paper as a filler, in amounts such that the surface of the paper itself comprises significant amounts of the salt. The surface need not be solid, i.e. flexible paper, cloth (suitably defatted, and treated if necessary to prevent evolution of gases in vacuo), metals and the like can be employed. For example, the sub strate may consist of a layer of the selected compound, evaporatively deposited uniformly upon the surface of a sheet of metal, such as a layer of silicon dioxide deposited upon an aluminum sheet by ordinary vapor vacuum coating or sputtering techniques.

i The ratio of particulate metal compound to hinder resin in the substrate surface coating can vary widely, ranging from about 3 to 15 or more parts of the powder to one part of binder. When the substrate is vaporcoated, of course, it is substantially uniformly coated.

While White or nearly white surfaces are preferred, light colored or even dark surfaces can be used since electronic read out may be employed, or the reflectivity of the deposited metal can be observed visually.

A latent image is formed upon the substrate by depositing on the surface, in the areas where the image is to be formed, a small amount of an aqueous fluid. The part of the liquid which is the operativev moiety seems to be water, since water alone, even conductivity water, produces the effect. It appears that any aqueous solution is suitable for the purpose of the invention so long as it is inert with respect to producing overt chemical changes in the substrate. The term overt is employed because it is not known what effect the imageforming solution has upon the substrate, since there is no apparent visible change. Nevertheless, the latent image formed is so stable that even though excess water has been evaporated from the surface, so that there is no visible trace of any image whatsoever, and even after the substrate bearing the latent image has been heated in an oven at 100 C. for 20 minutes, the latent image is still developed by vapor deposition of metal thereupon to form a visible permanent metallic record. Water is the simplest image forming agent which can be used, and other aqueous solutions, such as dilute ammonium hydroxide solution, dilute acetic acid solution and the like can be employed. However, so far as can be determined, there is no advantage in adding other substances to the water to be used for making the image, unless a preliminary visible latent image is to be produced, for the purpose of facilitating corrections and additions, if these should be necessary. For this purpose, small amounts of dyes can be incorporated into the aqueous liquid, in amount sufficient to render the latent image visible.

The formation of the latent image upon the substrate can take place by any suitable means for conveying the liquid to the surface, as, for example, the use of a printing plate, the surface of which is dampened with the treating liquid, use of brushes, linoleum printing blocks, relief images of all sorts, such as those produced in gelatin by wash-off relief, papier-mache relief images, wooden blocks and the like. It will be apparent that any means for depositing the latent image upon the surface in the areas in which the information is to be recorded will be suitable.

After deposition of the latent image forming liquid is completed, excess amounts, such as visible signs of liquid, are removed by evaporation. Very small amounts of water suffice to produce the effect and it is not necessary that visible liquid be present on the surface of the substrate in order to form the latent image. It is preferred that visible signs of moisture be avoided, particularly if the metallic salt present as the surface be somewhat water-soluble. It is suflicient merely to moisten the surface of a printing plate, for example and then press it to the surface of the substrate, which is of course suitably supported to ensure uniform contact. After removal of the visible moisture, if any, the substrate is ready for development of the visible image by vapor deposition. This may take place immediately, or the latent image can be stored without loss of its properties for so long as may be desired.

The metals which are employed for formation of the visible record by selective vapor-deposition are, as noted above, metals selected from Group II-B of the Periodic Table, which includes the metals magnesium, zinc, cadmium and mercury. It will be apparent that mercury is somewhat less desirable for formation of permanent images, but under suitable temperature conditions of deposition and storage, mercury can produce images of relative permanence, which may be important for the production of special effects.

The formation of the visible image takes place under the usual conditions of depositions of metals by vaporcoating techniques. The vapor coating can take place in the usual vapor coating apparatus comprising a vacuum chamber in which a coiled filament, say for example of tungsten, Nichrome or the like is employed to melt and vaporize a wire of the metal which is to be employed for vapor coating. Alternatively, a crucible containing the developing metal can be heated by suitable electrical means, to bring about evaporation of metal from the surface of the liquid metal in the crucible. The substrate to be coated is preferably located at a distance from the surface of the vapor-producing source which does not exceed approximately the mean free path of the coating molecule under the pressure conditions which exist in the chamber. Thus, pressures, in the range of about to 10* mm. of mercury can be used for vapor deposition purposes. If desired, a small amount of helium or argon may be introduced into the chamber to increase the pressure by one or two orders of magnitude. In this way the velocity at which the metallic vapors traverse the space between the vapor source and the substrate is reduced, and the contrast of the image deposited upon the substrate is increased. The same eifect can be obtained by other methods of slowing the vapor depositing metals, for example, by the use of a grid of proper charge or other electrostatic means interposed between the surface upon which the metal is to be deposited and the vapor coating source, or by increasing the substrate temperature slightly.

The time required for formation of the visible record depends upon several factors, for example, the area of the surface of molten metal which is exposed in the vapor coating source, the area of substrate to be covered, the temperature of the metal in the source, and the density required in the deposit and the accommodation coefficient of the surface. It has been found that 50 monolayers produce optical densities of about 1. Thicker layers of metal may be required for other purposes than simple visual inspection, as for example, in producing printed circuits. Thus, if the surface of the substrate in areas where no latent image is present readily accepts the depositing metal vapor, the time of deposition will have to be kept as short as possible in order to provide maximum contrast, for while the depositing metal selectively deposits upon the surface where the latent image is present, deposition is also proceeding under such circumstances upon the substrate itself, thereby producing increased background and lessened contrast. The actual time required in each case is determined by simple empirical experiment. Alternatively, means known to the art for estimating the optical density of the image, as for example, the inclusion in the vapor coating chamber of glass test plates upon which the metallic vapor condenses at the same time that the image is being formed, these test plates being inspected visually from time to time to determine the amount of absorption occasioned by the vapor deposit upon their surface.

The process of the invention is useful for producing both continuous and half-tone images: Thus, line images, reproductions of photographs by the half-tone process, continuous tone images produced by gelatin wash-01f relief processes and the like can be formed upon the substrates described. When the substrate is transparent (a thin film of the metal salt, for example, a layer which is only a few monolayers or less in thickness, being evaporatively deposited on a transparent plastic substrate such as methyl methacrylate, cellulose acetate, etc.), the image formed can be a diapostive or dianegative. The resulting record is adapted for optical projection. Furthermore, while simple visible records useful for optical readout may be produced by the method of the invention, the metallic images also have other and important uses in the field of microcircuitry, computer storage, printed circuits, and the like, and can if desired be read out electronically.

Having thus generally described the invention, the following specific examples will show the details of the process and the products thereby produced.

EXAMPLE 1 A piece of baryta paper (high quality rag stock, the surface of which is coated with a uniform film of barium sulfate containing a small amount of gelatin as a binder) was employed as a substrate. The surface of etched copper block bearing a line image was moistened and pressed against the surface of the baryta paper with uniform moderate pressure. Upon removal of the block, no image was visible. The paper was then placed in a vacuum-coating apparatus, in which the source of developing metal was a tungsten spiral in which was laid a short piece of zinc wire. The evaporation source was about 4 inches distant from the surface of the paper. The pressure in the apparatus was reduced to approximately 10- mm. of mercury, the filament was energized and under visual observation, vapor deposition was continued until a visible record of the line image of optical density about 1 was formed upon the surface of the baryta paper. The background remained substantially white, while the image produced varied from dark gray to black.

EXAMPLE 2 functional part of the surface thereof by depositing at least trace amounts of an aqueous fluid in areas where a latent image is to be formed, removing any visible moisture, and thereafter, while maintaining the said substrate in vacuo, exposing the said substrate to vapor deposition 5 A fiat sheet of paper laminated to a thin sheet of of a metal of the group consisting of magnesium, zinc, aluminum foil, upon the surface of which a uniform concadmium and mercury for a period of time sufficient to tinuous layer of zinc oxide with a Pliolite resin binder Pr duce a distinguishable image corresponding to said formed the upper surface, was employed. A copper printlat nt image. ing block bearing a halftone image was employed as the :1 2. The process for recording information which conprinting means. The surface of the printing block was sists essentially in the steps of producing an invisible latent slightly moistened by exposing it to water vapor d image upon a substantially inert, substantially anhydrous pressed upon the surface of the zinc oxide paper. The Solid Substrate having an inorgahie metal compound as a pressure employed was 10,000 pounds per square inch functional part of the surface thereof by depositing at and the printing block was pressed against the substrate least trace amounts of Water in areas where a latent image for about 3 minutes. The block was then removed from y is be formed, removing y Visible moisture, and therethe surface, and the substrate upon which there was no after, While maintaining the Said Substrate bearing the visible image, was placed in a vacuum coating chamber. Said latent image in vacuo, exposing the Said substrate to Under visual inspection, a positive visible image was dethe Vapor deposition of a metal of the gfOuP consisting of veloped upon the surface of the substrate, using zinc as a magnesium, Zine, cadmium and mercury for a Period of developing agent at a pressure of 10- mm. of mercury. time sufficient to produce a distinguishable image corre- The image corresponded to that image which would have Spending to Said latent imagebeen produced had the printing block been coated with The Process for recording information wh h ni t i k i th normal way sist essentially in the steps of producing an invisible latent The same result was obtained when pressure of 3,000 image p a substantially inert, substantially anhydrous pounds per square i h was employed f 3 minutes i sol d substrate which is substantially free from substances pressing the copper printing block against the substrate. Whlch evolve gases in Vaeuo and having an inol'ganie metal The same result could be obtained with some loss in compound Selected from the group consisting of Oxides, harpness of thg image by dampening the surface of the sulfides and halides as a functional part Of the surface printing block using a sponge dipped in distilled water, r y deposlfihg at least trace amounts of an agent d pressing th bl k against h paper using moderate comprislng water in areas of said substrate where a latent hand pressure. The images produced by any of these Image is to be formed, removing y Visible moisture, means ld b t d i a desiccator, i normal d and thereafter, while maintaining the said substrate bearair, without loss of the latent image. However, if the s tho Said latontimaso in v subjecting the said paper was moistened with Water uniformly over the enstrate to FPP dePOSmOII {hetal Chosen fr m th tire surface, or if exposed to air of high humidity for group 0f ihagheslunls Z1110, Cadmium and morlong periods of time, the latent image disappeared. 'Y a tlme sufiieleht to P o a distinguishable When cadmium or magnesium were used as the metallic age 111 areas Where Said lateht lfhage is P vapor sources to form the visible image, dark gray and The P e l'ecordlng information, which nblack images were f d in the Same way as when Zinc 40 sists essentially in the steps of producing an invisible latent was employed. image upon a substantially inert, solid, substantially an- The following table shows the results obtained with hydrous slfbstrate Whlch 1S s11bstah'llally free from various substrates and means for producing the latent stances Whlch evolve gases in vacuo, and having Zine OXide images following the procedure set forth above for deas a functional P of the Surface thereof, y depositing veloping the latent image to a visible record using vapor at least trace amounts of Water in areas h r a lat nt development with various metals. During development, image is to he formed, removing y Visible moisture, a the substrate was at room temperature unless otherwise thereafter subjecting the said substrate to vapor deposition specified. of zinc thereupon in vacuo, for a period of time sufficient Table I Means of Metal Substrate Latent image forming liquid forming image for devel- Result opment OdS-Pliolite on aluminum foil backed with Distilled water Glass stylus... Zn Strongblackimage paper. on yelow ZnO-Pliolite on aluminum foil backed with Conductivity water Artists brush- Zn Ol e' a t dark gray paper Dilute aqueous ammonium Glass stylus--- Cd Dia i lri gmy image.

hydroxide solution. Distilled water do Mg Light gray image. Dilute acetic acid Do. Dilute aqueous KOH soludo Very light gray tion. image. TiOz in gelatin binder, paper backing Distilled water Ctgglrligklgalit; Zn Dark gray image. Biz O3 in gelatin binder, paper backing Tap water Rubber stamp. Cd Do. S102, deposited in vacuo on aluminum sheet Distilled water.. Pttapiir 11111;??? Cd Gray image. Baryta paper Water vapor Co p iier line I Cd Dark gray image.

ma l'lX.

1 Development carried out while substrate heated to about 150200 C.

What is claimed is:

1. The process for recording information, which consists essentially in the steps of producing an invisible latent image upon a substantially inert, substantially anhydrous to produce a distinguishable image corresponding to said latent image.

5. The process for recording information which consists essentially in the steps of producing an invisible latent solid substrate having an inorganic metal compound as a image upon a substantially inert, substantially anhydrous 7 8 solid substrate which is substantially free from substances References Cited in the file of this patent which evolve gases in vacuo and having zinc oxide as a UNITED STATES PATENTS functional part of the surface thereof, by depositing at 1,843,572 MacGahan Fehz 1932 least trace amounts of water upon the said substrate in 2 054 Colbert et 1 Sept 1949 areas where a latent image is to be formed, removing any 5 2,883,257 Wehe Apr. 21, 1959 visible moisture, and thereafter subjecting the substrate FOREIGN PATENTS bearing the said latent image to vapor deposition of cad- 2 mium thereupon in vacuo, for a period of time suflicient 74 Germany Sept 1953 to produce a distinguishable image corresponding to said 10 OTHER REFERENCES latent image. Holland: Vacuum Deposition of Thin Films, 1956, pp.

180-482 and 257-263. 

1. THE PROCESS FOR RECORDING INFORMATIN, WHICH CONSISTS ESSENTAILLY IN THE STEPS OF PRODUCING AN INVIDSIBLE LATENT IMAGE UPON A SUBSTANTIALLY INERT, SUBSTANTIALLY ANHYDROUS SOLID SUBSTRATE HAVING AN INORGANIC METAL COMPOUND AS A FUNCTINAL PART OF THE SURFACE THEREOF BY DEPOSITING AT LEAST TRACE AMOUNTS OF AN AQUEOUS FLUID IN AREAS WHERE A LATENT IMAGE IS TO BE FORMED, REMOVING ANY VISIBLE MOISTURE, AND TEHREAFTER, WHILE MAINTAING THE SAID SUBSTRATE IN VACUO, EXPOSING THE SAID SUBSTRATE TO VAPOR DEPOSITION OF A METAL OF THE GROUP CONSISTING O FMAGNESIUM, ZINC, CADMIUM AND MERCURY FOR A PERIOD OF TIME SUFFICIENT TO PRODUCE A DISTINGUISHABLE IMAGE CORRESPONDING TO SAID LATENT IMAGE. 